1. Field of the Invention
This invention relates generally to the field of data networks with distributed line amplifiers and, more particularly, to the field of broadband communications networks.
2. Related Art
Broadband communication networks deliver data signals to homes and businesses throughout the world. The data signals may include, for example, television signals, telephone signals, radio signals, audio and video signals, Internet service, and/or other data and communication services. A typical broadband communication network includes a head-end or central reception point where satellite and/or off-air signals are collected, and processed. Data signals are injected and combined with the audio and video signals and are rebroadcast over a network. The network is typically made-up of coaxial cable (coax), optical fiber or a combination of coax and fiber known as hybrid fiber coax (HFC). The network may also include wireless connectivity for specific types of data. At the other end of the network are end-user subscribers. These may be residential subscribers, businesses or other networks.
Amplifiers are used throughout the broadband communication network to insure sufficient signal levels exist, for example, to meet regulatory standards set by the U.S. Federal Communications Commission (FCC) and requirements of equipment manufacturers. For example, a post-amplifier may be used between an off-air antenna and the head-end to increase the received signal to a strength (i.e., amplitude) sufficient for processing by the head-end. The head-end then uses channel processors, satellite receivers, modulators, decoders, encoders and a combining network to produce the signals that will be sent over a trunk network. The combining network provides broadband signals to one or more trunk amplifiers to create the origination point of the trunk network from the head-end. The trunk network includes one or more trunk lines. Each trunk line may be split into two or more discreet trunks. These trunks may be optical or coaxial based. Splitting of the trunk network is created by installing splitters or directional couplers in the trunk network, and continues throughout the network to provide the required network connectivity.
Distribution cables are connected to an optical node, trunk amplifier, distribution trunk amplifier (with a built in distribution amplifier), or line extender amplifier to create the distribution network. The distribution network uses splitters, couplers and distribution taps (tap) to provide signal to the customer. A service drop is connected to the tap and to a customer's on-premise equipment (CPE) to provide the data signals to the customer.
Each signal transmitted in a broadband communication network is typically assigned a unique channel or frequency within the operational bandwidth of the amplifier. The frequency spectrum of the signals transmitted in the broadband communication network is typically in the range of 5 MHz to 862 MHz. The bandwidth used for the reverse path is typically found in U.S. NTSC networks in the 5-42 MHz range, while most analog signals for the forward path are in the 50-550 MHz range, and the digital signals are found in the 550 MHz to 862 MHz range.
European signals are normally in a PAL format and operate between 5 MHz and 862 MHz also. The bandwidth allocated for the reverse path is in the 5 MHz to 65 MHz band, while remaining bandwidth is in the 80 MHz to 862 MHz range. Systems may be all analog, all digital or any combinations thereof.
As these signals propagate through the cable(s), the signals will be attenuated. At some point, the attenuation will result in a loss of data. Thus, additional amplification is required between amplifiers to insure sufficient signal strength is available to provide the data as required by the FCC and by equipment manufacturers. This process of re-amplification insures that the quality of signal coming from the head-end is maintained throughout the network to the customer's premise. This additional amplification is achieved using trunk amplifiers; trunk amplifiers with built-in distribution amplifiers; and line extender amplifiers. As used herein, the term “line amplifier” refers to any amplifier used to amplify data signals in a broadband communication or other network.
To produce a useful amplified signal, each amplifier in the broadband communication system requires a viable input signal (i.e., a signal from which data is still detectable) and a power supply. The power supply provides the electrical power at the required voltage and current levels to power the electronic circuitry of the amplifier. For example, the power supplies typically output 60 Volts AC at 15 Amps. However, some power systems use variations of the 60 Volt power supply along with variations of a 90 Volt, 15 Amp or 25 Amp design. The amplifier will then use an internal power circuit to convert the AC to the required DC voltage for powering its internal circuitry.
Power failure to an amplifier will result in loss of the data signals at downstream and upstream points. To guard against such power failure, three techniques have commonly been used. First, an uninterruptible power supply (UPS) that uses backup batteries can be used. Second, backup generator systems have been used with and without UPS power supplies at specific power supply locations. Third, switching circuits have been used to provide power from a backup source upon failure of a primary source. Backup battery or backup generator systems are costly and have high-maintenance requirements.
Switching systems operate on the following principle. It is often the case that the amplifier power supplies, which are spatially separated along a broadband communication network, are powered by different service areas of the commercial power network. Thus, while one service area may fail, a neighboring service area may still be functioning properly. A common example of this phenomenon can be seen during a power outage, wherein buildings on one side of a street may have power, while buildings on the other side might not have power. In the case of a broadband communication network, in the event of a power failure at amplifier A (being supplied by grid #1), a power switch can be used to route the power from a distant power supply at amplifier B (being supplied by grid #2) along the cable to power amplifier A. To accomplish this, a power switch is associated with each power supply. Upon failure of a local power supply, the power switch will receive power from a remote power supply and provide the power to the local amplifier. The power from the remote power supply is transmitted between the power switches over the broadband communication network. Power combiners (also called, power inserters) are used to combine the power (AC) with the RF signals for transmission on the cable. U.S. Pat. No. 5,747,888 to Zilberberg is an example of a power switch.
What is needed is a power switch for use in a broadband communication network that improves upon existing power switches.